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51.
Busacca CA Grossbach D Campbell SJ Dong Y Eriksson MC Harris RE Jones PJ Kim JY Lorenz JC McKellop KB O'Brien EM Qiu F Simpson RD Smith L So RC Spinelli EM Vitous J Zavattaro C 《The Journal of organic chemistry》2004,69(16):5187-5195
The Boehringer-Ingelheim phosphinoimidazoline (BIPI) ligands were applied to the formation of chiral quaternary centers in the asymmetric Heck reaction. Several different substrates were examined in detail, using more than 70 members of this new ligand class. Hammett relationships were determined through systematic variation of the ligand electronics. All substrates showed essentially the same Hammett behavior, where enantioselectivity increased as the ligands were made more electron-deficient. Ligand optimization has led to catalysts which give the highest enantioselectivities reported to date for these difficult systems. 相似文献
52.
Dionigi C Nozar P Di Domenico D Calestani G 《Journal of colloid and interface science》2004,275(2):445-449
In this paper we propose a simple model for the formation of monodisperse polymer colloids, which provides a convenient set of synthetic parameters for given bead diameters. We provide experimental data in support of this model. 相似文献
53.
Mimmi MC Gullotti M Santagostini L Battaini G Monzani E Pagliarin R Zoppellaro G Casella L 《Dalton transactions (Cambridge, England : 2003)》2004,(14):2192-2201
The dinuclear and trinuclear Cu(II) complexes of an octadentate ligand derived from (S)-1,1'-binaphthyl-2,2'-diamine have been prepared and characterized by UV/Vis, CD, EPR and NMR spectroscopy. The ligand contains two tridentate aminobis(benzimidazole) donor arms connected to a central bidentate diaminobinaphthyl linker, which hosts the chiral unit. In the dinuclear Cu complex the ligation occurs essentially within the tridentate arms of the ligand. The two Cu centers are EPR nonequivalent and noninteracting. The EPR data suggests that one of the Cu ions additionally interacts with one of the tertiary aminonaphthyl donors. In the trinuclear complex the two aminonaphthyl donors bind the third Cu ion. The EPR spectrum of this complex shows the signal for a mononuclear Cu(II) center bound to a tridentate arm, while the remaining two Cu(II) centers are coupled through hydroxo groups. The CD spectrum shows that in the free ligand a severe reduction of the dihedral angle between the naphthyl groups from the strain free range occurs. This conformation is stabilized by ring stacking interactions with the benzimidazole groups. On complex formation this interaction is removed because the benzimidazole groups are involved in metal binding. In the dinuclear Cu complex the conformation of the binaphthyl chromophore probably approaches the strain free range, while in the trinuclear Cu complex a marked flattening of the dihedral angle between the two naphthyl rings occurs. Both complexes are active catalysts in the oxidation of L-/D-Dopa derivatives to quinones. High enantioselectivity is observed in the oxidation of L-/D-Dopa methyl ester catalyzed by the dinuclear Cu complex, which exhibits strong preference for the d enantiomer. The enantioselectivity is largely lost for the trinuclear Cu complex. 相似文献
54.
We study the entanglement properties of the output state of a universal cloning machine. We analyse in particular bipartite and tripartite entanglement of the clones, and discuss the classical limit of infinitely many output copies. 相似文献
55.
The study of the transport mechanisms connected to solid-liquid interactions is fundamental in the determination of the extension of the pollution of a site and in the evaluation of the best remediation process to be applied. The sorption of hydrophobic ionizable organic contaminants from the groundwaters is supervised not only by the physico-chemical properties of soil and pollutants, but also by the groundwaters pH, which deeply influences their solubility in the aqueous media, and consequently their transport mechanisms in the aquifer. In this work an experimental study of the sorption of phenol and 2-nitrophenol on two soils, different in particle-size distribution, CEC and organic carbon content, was realized. The sorption potential of the soils was evaluated by means of a physical, mineralogical and chemical characterization. The experimental data coming from some batch tests, performed at pH values equal to 4, 7 and 10 were fitted by means of linear, Freundlich and Langmuir isotherms models. The soil-contaminants interaction mechanisms that influence the isotherms shapes were then analyzed and discussed, and a comparison between the theoretical and experimental values of the partitioning coefficient KD was performed. 相似文献
56.
Cossu S Cimenti C Peluso P Paulon A De Lucchi O 《Angewandte Chemie (International ed. in English)》2001,40(21):4086-4089
57.
M. Eugenia Pérez‐Ojeda Dr. Beatriz Trastoy Álvaro Rol Dr. María D. Chiara Prof. Dr. Inmaculada García‐Moreno Dr. Jose Luis Chiara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(21):6630-6640
A general procedure for the assembly of hetero‐bifunctional cubic silsesquioxanes with diverse functionality and a perfectly controlled distribution of functional groups on the inorganic framework has been developed. The method is based on a two‐step sequence of mono‐ and hepta‐functionalization through the ligand‐accelerated copper(I)‐catalyzed azide–alkyne cycloaddition of a readily available octaazido cubic silsesquioxane. The stoichiometry of the reactants and the law of binomial distribution essentially determine the selectivity of the key monofunctionalization reaction when a copper catalyst with strong donor ligands is used. The methodology has been applied to the preparation of a set of bifunctional nano‐building‐blocks with orthogonal reactivity for the controlled assembly of precisely defined hybrid nanomaterials and a fluorescent multivalent probe for application in targeted cell‐imaging. The inorganic cage provides an improved photostability to the covalently attached dye as well as a convenient framework for the 3D multivalent display of the pendant epitopes. Thus, fluorescent bioprobes based on well‐defined cubic silsesquioxanes offer interesting advantages over more conventional fully organic analogues and ill‐defined hybrid nanoparticles and promise to become powerful tools for the study of cell biology and for biomedical applications. 相似文献
58.
Together we glow: Fully organic host-guest crystals with two dyes inserted in their parallel nanochannels display broad emission in the visible range thanks to resonant energy transfer. The conjugated host crystal provides light harvesting in the UV region. 相似文献
59.
Daniele Cauzzi Claudia Graiff Chiara Massera Giovanni Predieri Antonio Tiripicchio 《Journal of Cluster Science》2001,12(1):259-271
The reaction of [Ru3(CO)12] with Ph2(pyth)PSe (pyth=5-(2-pyridyl)-2-thienyl) allows to obtain two novel clusters [Ru3(3-Se)2(CO)7{P(pyth)Ph2}2] 1 and [Ru3(3-Se)(-PPh2)(-pyth)(CO)6{P(pyth)Ph2}] 2 in satisfactory yields. The first one exhibits the well-known bicapped, open triangular, 50-electron nido-core, whereas 2, whose crystal structure has been determined, shows the rather rare Ru3Se tetrahedron with the Ph2P and pyth fragments as side-bridging ligands. Morever cluster 2 belongs to the exiguous family of selenido-phosphido clusters not easily achievable by other routes. 相似文献
60.
The syntheses of several differently substituted amides formally derived from a chiral amine, either E-2-(2-hydroxyphenyl)cinnamic acid or both E- and Z-2-(2-hydroxynaphthyl)cinnamic acid, are reported. These molecules display a restricted rotation about the C2-Caryl bond. The barriers to rotation about the C2-Caryl bond were measured by the dynamic 1H NMR and were found to vary between 11.8 and 24.5 kcal mol−1, depending on the substitution. In particular, E-2-(2-hydroxynapthyl)cinnamic amides, displayed a high barrier to rotation (ΔGc‡=24.4 kcal mol−1) and could be isolated in both diastereomerically pure forms at room temperature. The X-ray structure of one E-2-(2-hydroxynapthyl)cinnamic amide, was resolved, enabling for the determination of the absolute configuration of the chiral axis (aR). 相似文献